The invention relates to trammel-and-beam instruments and it is concerned with beam compasses (also known as rules) of the type including a compass beam and one or more removable trammels. More specifically, the invention relates to an adaptor that can be removably secured on a square head to provide the square head with structure that allows it to function as a trammel.
Trammels have been known or existed for many years. The Christian U.S. Pat. No. 314,316 discloses a draftsman's tool having a rule which is marked on its face with a scale in inches or centimeters and fractions thereof, or any other scale. Two slides are mounted on the rule and they may be adjusted longitudinally. Each slide supports structure holding a needlepoint or a pencil.
The Jooss U.S. Pat. No. 1,321,312 is directed to a combination tool having a machinist blade or ruler and a fixture mounted on one edge of the ruler and a moveable member. The combination tool is utilized as a marking tool for producing parallel lines and the distance between can be definitively measured upon the scale of the ruler.
The Vane U.S. Pat. No. 2,309,809 is directed to a geometrical instrument having a ruler beam with first and second riders mounted on the beam. The Hart U.S. Pat. No. 2,645,022 is directed to a trammel and beam instrument having two moveable trammel heads mounted on the beam.
The Asperger U.S. Pat. No. 2,824,377 is directed to a geometrical instrument. It has a blade and two trammel heads each having an indicator leg extending from their bottom end. It may also have a scribe attached in one of the trammel heads.
It is an object of the invention to provide a novel structure that can turn a square head into a trammel.
It is also an object of the invention to provide a novel trammel adaptor that can be easily and quickly mounted on a square head or removed from a square head.
It is another object of the invention to provide a novel trammel for a square head that is economical to manufacture and market.